Succinic acid and its derivatives are useful platform chemicals that are widely used in the manufacturing of polymers, fuel additives, inks, cosmetics, and as additives in foods and pharmaceuticals. For example, succinic acid can be used as an input In the production of pigments, solvents, detergents, metal plating and polybutylene succinate polymers, which can be used to replace conventional plastics in applications such as flexible packaging, agricultural films and compostable bags.
Succinic acid has been traditionally produced from petrochemicals which are limited, costly and cause pollution problems. One to the variety of* applications, alternative methods of producing bio-succinic acid have received attention in the past few years. A more environmentally friendly approach that has gained much interest is the fermentative production of succinic acid from glucose by anaerobic bacteria. The fermentative production of succinic acid can be regarded as a green technology not only because renewable substrates are used for its production, but also CO2 is incorporated into succinic acid during fermentation. Thus, fermentative succinic acid contributes a green, bio-derived feedstock for the manufacture of synthetic resins, biodegradable polymers, and chemical intermediates.
Although the fermentative production of succinic acid has several advantages over petrochemical-based processes, for the biotechnological process to be competitive with petrochemical production one desires to minimize the production costs. (See e.g., James McKinlay et al., “Prospects for a Bio-based Succinate Industry,” APPL. MICROBIOL. BIOTECHINOL, (2007) 76:727-740; incorporated herein by reference). About 60% of the total production costs are generated by downstream processing, e.g., the isolation and purification of the product in the fermentation broth. The purification of succinic acid from fermentation broths is a critical step in the development of a successful, cost effective process to recover the acid.
Over the years, various approaches have been developed to isolate succinic acid. These techniques have involved using ultra-filtration, precipitation with calcium hydroxide or ammonia, crystallization, electrodialysis, liquid-liquid extraction, sorption and ion exchange chromatography. (See, Tanja Kurzrock et al., “Recover of Succinic Acid from Fermentation Broth,” Review, BIOTECHNOLOGY LETTER, (2010) 32:331-339; incorporated herein by reference.) A variety of impurities including salts, organic acids and remaining biomass all can inhibit the isolation of pure succinic acid or downstream processing of succinic acid containing streams. Because of this, a variety of different solutions have been proposed for the purification of succinic acid, but these solutions have disadvantages.
For instance, a problem with some prescriptions that others have explored is the relatively limited capacity of conventional ion exchange solutions to separate the desired succinic acid. Ion exchange has not been proven a viable processing technique that, can be translated to commercial scale operations. To date, resins have not been shown to have a large enough capacity for succinic acid to provide an efficient sorption process. Hence, adsorption chromatography has been limited by both selectivity and capacity for succinic acid. The use of ion-exchange to remove salts for the fermtentation stream could be applied, but requires the use of acids and bases to regenerate the resins and is only efficient if relatively low levels of salts are present. If the salt content is high in a fermentation broth, an ion exchange system would be retarded and inefficient because of low throughput. Hence, ion exchange resins will be less efficient to separate the salt from other organic acids. Therefore, this is not efficient in cases with high levels of salts. Moreover, traditional ion exchange techniques do not separate easily the different organic acids present in the broth. Electro-deionization (EDI) does not separate the different organic acids to a degree feasible for high-throughput applications because of issues associated with membrane fouling. Other approaches such as reactive extraction require organic solvents and expensive reagents.
Even though all of these techniques have had some success, they have been limited either by cost, byproduct-waste generation, or economy of scale. Hence, for these reasons, a need exists for better or more direct methods for recovery of succinic acid, which can simplify the process and reduce downstream processing costs as well as waste.